Current video projectors can be categorized into three quite distinct technologies. The first uses a two-dimensional scanning system to direct a beam of electrons or photons onto a phosphorescent layer of material which emits visible light as a function of the intensity of the incident beam. The light can be collected by a lens system and focused on a screen to form an image. The most common example of this category is the CRT projector. These projectors are limited in their resolution capabilities by the need to focus the incident beams onto a sufficiently small spot, the thickness of the light emitting material and the bandwidth of the modulation drive electronics.
The second category eliminates the scanning beam by using a directly addressable two-dimensional array to activate the phosphorescent material. Examples of such devices are organic light emitting diode displays (OLED'S). These displays are limited in their resolution capabilities by the difficulties in manufacturing two-dimensional arrays with very large numbers of individually addressable elements.
The third category is known as light valves. These do not emit light directly from a scanned phosphorescent material but, as their name implies, use a two-dimensional scanned array to modulate a light beam from a light source such as an arc lamp. Early light valves such as the Eidophor or the Talaria used scanned beams of electrons to modulate the transmission or reflection of the light valve materials. Current systems use digitally addressable two-dimensional arrays to modulate the optical characteristics of each addressable element of the light valve which is usually a thin layer of liquid crystal material. The resolution of these devices is also limited by the difficulty in making two-dimensional arrays with very large numbers of individually addressable elements.
Also, micro electro mechanical (MEM) devices are finding uses in the display industry. Digital light processing (DLP) technology, such as manufactured by Texas Instrument, is used by many display manufacturers using MEM technology to create a two-dimensional array of tiny mirrors to form a digitally addressed light valve system. Similar products are also manufactured by other companies.
The grating light valve (GLV), such as described in U.S. Pat. No. 5,331,360, uses a similar concept but it uses a diffractive grating rather than a reflecting mirror surface to perform the modulation functions. This grating uses strips of material which are only 3 microns in width. Manufacturing tolerances can create significant differences in the optical characteristics of adjacent pixels.